Temporal and Spatial Dynamic Distribution of Cotton-Wheat Composite Root System under Condition of Cotton-Wheat Double Cropping System

Cotton-wheat double cropping system is a main planting system in cotton cropping zones in China, but less research has been done in soil nutrient competition while more in light competition of up ground part of composite population in the symbiotic period of wheat-cotton. Under the condition of high yielding cotton-wheat double cropping system, contrasting to the monoculture cotton(C) and the monoculture wheat, the temporal and spatial dynamic distribution of cotton-wheat composite root system(C-W) was studied with drill and DT-SCAN Scanner. The results showed that the root length, root length density, root surface area and root average diameter of cotton in C and C-W had a single-peak curve of changes (during) the whole growth stage. In soil layer below 40 cm, the decline speed of root surface area, root length and root length density of cotton in C-W was obviously lower than in C after blooming stage, and difference of root average diameter was little. The root dry weight of C-W was lower than C before blooming stage in upper layer of soil, but obviously higher than that in deeper layer after blooming stage and the total amount of roots was mere in C-W than in C. Within the distance of 25 cm from cotton plant, the biggest root length, root length density and root surface area were in 0-20 cm soil layer, and descended with the deepening of soil layers. The upper layer root length and root length density were decreased in C and increased in C-W with increasing the distance from cotton plant; and the maximum of them were at the location of 12.5 cm from cotton plant in C but 3.75 cm in C-W. The localities with max value of root length density in every layer were farther from cotton plant with deepening the soil layers. Root surface area spatial-distribution was the same as root length density. At the location of 3.75 cm from cotton plant, root average diameter was decreased with deepening soil layers, while at the locations of 12.5 cm and 21.25 cm from cotton plant, root average diameter increased in 0-40 cm soil layer and decreased in soil layers below 40 cm with the deepening of soil layer. The localities with maximum root dry weight in every layer of C distributed like a bow with vertical taproot as bowstring, and those of cotton in C-W were farther from cotton plant.